The present invention relates to a method of rearing a bird of germ-free status. It further relates to the production of avian eggs of germ-free status. It also relates to a method of producing various eggs and birds.
In this specification, the term xe2x80x9cgerm-freexe2x80x9d is used very broadly and relates to many pathogens and infections that can be carried by birds, particularly, poultry such as chickens and turkeys which are used widely to produce flocks of birds for breeding to produce fertile eggs for commercial production and to produce eggs and meat for human consumption. Further, such eggs and birds are used in the manufacture of a wide range of biological substances including vaccines, fibroblasts and proteins, both for therapeutic and prophylactic use in people and animals. Poultry, particularly hens, is used extensively for these tasks. They are further used extensively for diagnostic tests and the production of transgenic eggs and birds. Many of these uses require eggs and/or the birds produced from them to be free of all contaminants such as infections, including a variety of species of parasite, bacteria, mycoplasma, viruses, retroviruses, prions, DNA and RNA fragments. Sometimes, the viruses can be small viruses including picoma and parvo viruses. Some of the bacteria from which eggs are often contaminated include Clostridia and Enterobacteria. There are many nonpathogenic organisms that should be controlled. Similarly, many of the micro-organisms which include parasites, aerobic and anaerobic bacteria, commensal species and species associated with the gut, are undesirable. Similarly, mycoplasma, viruses including retroviruses, prions, fungi, yeast and moulds are also undesirable.
Therefore, the term xe2x80x9cgerm-free statusxe2x80x9d includes all of these and is much broader than just free of specified pathogens. For example, conventional specific pathogen free (SPF) are not specified free from some viruses and indeed can be contaminated with bacteria and indeed for certain uses, these may be sufficient. The use to which the eggs and the birds are to be put will determine the contaminants that the egg or bird must be free of. Conventional contaminant free and some SPF eggs are derived by treating fresh naturally laid eggs with chemicals, including disinfectants and antibiotics, and placing them in isolators. Such naturally laid eggs are taken from selected parent stock birds. While these methods have been relatively successful in the production of SPF eggs, they have not been truly successful in producing what are germ-free eggs as the chemicals are not able to eliminate contamination from, for example, bacteria entering the pores of the eggshell immediately after laying and before disinfection. Contamination of eggs results in loss of compliance with specifications and, in many instances, loss of commercial value and utility.
Additionally, the term xe2x80x9csimilarxe2x80x9d is used in a broad sense and could refer to the same species or indeed, could be not the same species that had been reared together naturally for some considerable time, or might not, for example, be the same species but might have some other similarity that was required. Thus, they might not be of a particular species but might have effectively been grown naturally over many years to form a flock that could be described as similar.
U.S. Pat. Specification No. 5,011,780 (Margaret Mary Perry) describes an in vitro avian embryo culture technique which, while not particularly applicable to the present invention, describes in some detail the embryonic development of eggs. This specification is directed to the incubation of an embryo in a closed container after the embryo has been removed from its shell. Indeed, in this specification, the container used is preferably part of an egg shell which has been chosen from the same species as is being cultured or, in the terms of the present invention, from a similar hen. This invention is directed towards the genetic engineering of poultry but also to the investigation of fundamental mechanisms of avian development. It is directed towards providing an alternative to surgical intervention in the laying hen.
Similarly, U.S. Pat. Specification No. 5286641 (Naito et al) discloses an in vitro culture method for a fertilized ovum of a hen in which an embryo which has just been fertilized is taken from an upper portion of the magnum of the oviduct of a hen within an hour or so after oviposition and then subsequently cultured. However, both of these specifications merely disclose the artificial culturing of eggs and do not deal with the purpose of the present invention.
The present invention is directed towards providing eggs of germ-free status to allow various diagnostic tests to be performed. Further, the invention is directed towards providing eggs and birds that could be used in the manufacture of a wide range of biological substances. Thus, the invention is directed towards providing both eggs and birds which are free of all contaminants such as infections, including a variety of species of parasites, bacteria, mycoplasma, viruses, retroviruses, prions, DNA and RNA fragments.
Indeed, it is an object of the present invention to produce, what are effectively sterile eggs and hens which could be used as food, in certain specified situations for particularly delicate patients.
The invention provides a method of rearing a bird of germ-free status. The method comprises choosing a bird and housing it as a parent bird and then removing the egg from the parent bird prior to the transfer of the egg to the cloaca in the parent bird, thus avoiding most contaminants to the egg that would normally occur within the parent bird. As an eggshell is porous external contamination is a major problem. Then, the egg is incubated in a sterile environment and hatched to produce a laying bird. Generally speaking, these laying birds will all come from the one flock of similar birds, all reared under the same conditions. They may, for example, be hatched naturally in a sterile environment. The flock may already be a flock of birds which are of a particular contaminant free status which may have been produced, for example, by natural selection under controlled conditions. The whole purpose is to provide germ-free birds. Very often, therefore, samples of the laying birds will be removed and tested for specific contaminants to provide a measure of the germ-free status. By an iterative process, it will be possible to eventually produce a flock of birds which will be virtually sterile and of a germ-free status. Thus, initially, when the laying birds are produced, they will not form a flock of sufficiently germ-free status and it will be necessary to continue the process until birds of the desired germ-free status are obtained.
In accordance with the invention, the egg is surgically removed from the parent bird by aseptic surgical laparotomy. Thus, the birds are euthanased and then the surgical operation is performed.
The surgical operation, in one method according to the invention, comprises:
performing a laparotomy incision and tying off the oviduct of the bird at both ends with sutures;
transecting the oviduct distal to each suture;
removing the egg enclosed in the oviduct;
sterilising the oviduct;
removing the egg; and
sterilising the egg.
The eggs are generally removed at a time prior to and as close as possible to the transfer time when the egg would naturally transfer to the cloaca and thus the laying pattern of a parent bird will often be recorded over time to ensure that this is done as close to the estimated transfer time as possible.
Indeed, the sterility can be further improved by feeding the laying birds, in the sterile environment, with food containing normal gutflora or sterile food. It will be appreciated that when birds are hatched which are not laying birds, they will then be retained for subsequent fertilisation of the laying birds. In this way, the whole flock can be sterile.
It will be possible, in the present invention, to produce simply the eggs for subsequent use. When eggs are required of a germ-free status, the first thing to do is to incubate the eggs by using the desired parent birds. Then, when the parent birds have been tested for specified contaminants to provide a measure of the germ-free status, house that laying bird in another sterile environment and use that laying bird to lay eggs which will have a germ-free status.
Preferably, on laying, the outer shell of the egg is sterilised.